1. Field of the Invention
This invention relates to novel amorphous alloys which are equipped with excellent properties such as a high corrosion resistance and wear resistance and are usable in various industrial and civil fields and in chemical plants.
2. Description of the Prior Art
A variety of amorphous alloys have been reported in recent years, which can exhibit excellent corrosion resistance not available from crystalline alloys. Roughly dividing these amorphous alloys, they can be classified into two kinds, one being metal-semi-metal amorphous alloys and the other metal-metal amorphous alloys. The former are of the alloy systems that contain Cr as an element imparting corrosion resistance, one or more transition metals, such as Fe, Ni an Co, as principal elements, and 15 to 20 atomic % of a semi-metal, such as P or C, as an element for amorphyzing the alloys. The latter are alloys composed of one or more elements of IVa and Va groups of the periodic table as elements effective for corrosion resistance, such as Ti, Zr, Nb and/or Ta, in combination with Ni (VIII group) or Cu (Ib group).
As is apparent from these examples, the highly corrosion-resistant amorphous alloys reported to date require the addition of a semi-metal where Cr is contained. Where metal-metal alloys contain Ti, it has been possible to realize high corrosion resistance only by combinations of elements belonging to groups which are far apart from each other in the periodic table.
An object of the present invention is to provide alloys composed of Ti or Zr and Cr and alloys composed of the first-mentioned alloys with one or more additional elements represented by M (at least one element selected from the group consisting of Mg, Al, Fe, Co, Ni, Cu, Mo and W) not as chemically heterogeneous crystalline alloys but as homogeneous amorphous alloys having high corrosion resistance and high wear resistance.
An alloy is generally crystalline in a solid state. When the composition of an alloy is limited and a method which does not develop long-range regularity in the atomic arrangement is applied in the course of formation of a solid, for example, the alloy is subjected to superquench solidification from a molten state, an amorphous structure having no crystalline structure and resembling a liquid is obtained. Such an alloy is called an "amorphous alloy". An amorphous alloy is homogeneous single-phase alloy in the form of a supersaturated solid solution in many instance, has substantially higher strength than the conventionally used metals and, depending on its composition, exhibits various properties led by extraordinarily high corrosion resistance.
The present inventors have proceeded with extensive research on the properties,of amorphous alloys not reported before. As a result, it has already been found that one or more elements of IVa and/or Va groups, such as Ti, Zr, Ta and/or Nb, can be combined with Al or Cu into an amorphous alloy by using sputtering techniques, which does not require melting, in the course of the formation of the alloy and the resulting alloy has excellent corrosion resistance. Some of these alloys have already been proposed in Japanese Patent Application Nos. 63-51567, 63-51568 and 63-260020. Japanese Patent Application No. 63-260020 is directed to the following two inventive aspects.
(1) A highly corrosion-resistant amorphous aluminum alloy comprising 25 to 60 atomic % Ti, the remainder being substantially Al. PA1 (2) A highly corrosion-resistant amorphous aluminum alloy comprising 25 to 60 atomic %, in total, of one or more of Mo, W, Ta and Nb and Ti, the content of one more of Mo, W, Ta and Nb being not more than 5 atomic %, the remainder being substantially Al. PA1 (1) An amorphous aluminum alloy comprising 10 to 75 atomic % Zr, the remainder being substantially Al. PA1 (2) A highly corrosion-resistant amorphous aluminum alloy comprising 10 to 75 atomic %, in total, of Zr and Ti, the content of Zr being not less than 5 atomic %, the remainder being substantially Al. PA1 (3) A highly corrosion-resistant amorphous aluminum alloy comprising 10 to 75 atomic %, in total, of one or more of Mo, W, Ta and Nb and Zr, the content of one or more of Mo, W, Ta and Nb being less than 5 atomic %, the remainder being substantially Al. PA1 (1) A highly corrosion-resistant amorphous alloy comprising 30 to 75 atomic % Cr, the remainder substantially comprising at least one element selected from the group consisting of Ti and Zr. PA1 (2) A highly corrosion-resistant amorphous alloy represented by the following formula: EQU X.sub.a Cr.sub.b M.sub.c
It has also already been found that Al can also form an amorphous alloy together with Zr by using a sputtering technique, that an Al alloy containing Zr and Ti can be obtained as a homogeneous amorphous alloy, that an alloy containing Zr as a principal alloying element in combination with a high melting-point metal such as Mo, W, Ta or Nb can be prepared as an amorphous alloy, and that all of these alloys are highly corrosion-resistant amorphous alloys which can form a protective film which is stable even in a severe corrosive environment such as hydrochloric acid or a solution containing chlorine ions and can hence be spontaneously passive. Based on these findings, Japanese Patent Application No. 1-101768 was filed. Japanese Patent Application No. 1-101768 is directed to the following three inventive aspects.
The amorphous alloys described above are all composed of Al, which is inferior in corrosion resistance, and Ti and Zr, which both impart high corrosion resistance. Still better properties can be expected if an amorphous alloy comprising a combination of elements having excellent corrosion resistance can be provided.
Ti and Zr show excellent corrosion resistance in a neutral environment land also in an oxidative environment. Ti exhibits its effectiveness in improving pitting corrosion resistance, especially in an environment where chlorine ions are contained. On the other hand, Cr, when present in an amorphous state, is known to exhibit superb corrosion resistance, even in a poorly oxidizing environment such as hydrochloric acid. Success in the formation of an amorphous alloy, rather than a chemically heterogeneous crystalline alloy, from these elements having such excellent corrosion resistance is expected to assure a wide variety of utility as a new corrosion-resistant alloy suitable for numerous environments.
Ti or Zr and Cr, however, belong to IVa group and VIa group, respectively, and are hence close to each other in position. Their formation into an amorphous alloy has therefore been said to be difficult, even when a semi-metal is added, to say nothing of the metal-metal system. The object of this invention is therefore to overcome the above difficulty, thereby providing an amorphous alloy composed of Ti or Zr and Cr as well as an amorphous alloy composed of the first-mentioned amorphous alloying elements and one or more of various metallic elements added thereto.